Seals of various types and shapes are employed to prevent fluid from escaping from a joint along a fluid flow path or in a fluid container. Joints in the flow path or in a container are of course formed whenever two or more members are brought together to form a continuous conduit or a fluid receptacle. One common type of seals are ring seals which are employed between members along the flow path or comprising a container to seal the gap between the two members, thus preventing fluid from escaping from between the two members. These two members often have grooves formed therein to receive the ring seal.
These ring seals are resilient due to their material and their geometric design, so that the ring seal fills the gap between the adjacent members defining the flow path. The desired result is that the ring seal will firmly abut both members at all points along the seal so that the gap is completely blocked by the ring seal.
Ring seals, while requiring a fairly wide radial dimension in order to achieve the desired flexibility, are sometimes designed to fit in very narrow annular spaces. The combination of this requirement and the accumulation of manufacturing tolerances on seal and groove diameters and widths can result in undesirable compromises and problems. To overcome these problems, split ring seals were developed to provide circumferential flexibility of the ring seals. Because of this circumferential flexibility, these split ring seals can be adjusted to fit in grooves which are only slightly wider than their radial dimension; thus eliminating the effects of seal and groove diameter tolerances. Other advantages of split ring seals are their ability to compensate for the effects of differential thermal expansion between the seal and the members forming the joint (thus avoiding circumferential thermal stresses) and the possibility of "springing" the seal open, so that it can be assembled over components which are larger in diameter than the seal groove (in the same way as piston rings are expandable to slip over the outside diameters of pistons until they can drop or snap into their recessed grooves).
A split ring seal is basically a continuous ring seal which has had a portion removed across a transverse cross section such that the ring seal can be opened at this split. Two free ends are formed by the split.
However, a split ring seal has the disadvantage that if the split ring is expanded such that the free ends are out of contact, a gap is formed between the free ends of the ring seal. Fluid can then escape through the gap. Thus, a simple split ring seal does not provide a complete seal under all pressures and temperatures, as is often desirable.
In response to this problem, split ring seals with slip joints have been developed. In these seals, the split ring seal assembly includes a slip joint formed by the ends of the split ring seal and a slidable element. The slidable element is in the shape of a ring segment having approximately the same curvature as the split ring seal. A first end of the slidable element is fixedly attached to the first free end of the split ring seal. The second end of the slidable element is slidably received within the second free end of the split ring seal. In these split ring seal assemblies, the second end of the slidable element slides within the split ring seal as the split ring seal assembly expands and contracts when subjected to varying temperatures and pressures.
An example of these ring seals is disclosed in U.S. Pat. No. 4,477,086, issued Oct. 16, 1984 to Feder et al. However, the ring seal assemblies disclosed in U.S. Pat. No. 4,477,086 have a number of disadvantages and are still inadequate for a number of reasons. First, this patent discloses that the split ring seal and the slidable element are of the same material and thickness. This design results in a slip joint which is relatively difficult to compress and not as resilient as desired. Also, since the split ring seal and the slidable element are the same thickness, the slidable element is more highly stressed than the ring seal due to the shorter dimensions of the slidable element and is easily compressed beyond its elastic limit. This is undesirable, as it results in relaxation of the joint elements which permits an increase in leakage through the joint which partially offets the advantages of using a slip joint.
Ring seals having an "E" cross section are well known in the art (see for example, U.S. Pat. No. 3,797,836 entitled SEALING RING issued to Horace P. Halling on Mar. 19, 1974 and U.S. Pat. No. 3,857,572 entitled E-RING SEAL ASSEMBLY issued to Dudley D. Taylor et al on Dec. 31, 1974). In many applications, these ring seals having E-shaped cross sections are preferable because they provide a more effective and stronger seal between the members comprising the flow path. Moreover, seals of the E-shaped cross section may be constructed from a relatively thin metal or other material such that the load required to deflect and compress the seal is lower than for ring seals of other shapes. Also, since the fluid pressure can energize the seal between the outer flanges and the middle arm of the E-cross section, the fluids actually help the seal perform its function.
It is apparent that there still exists a need in the art for a ring seal which can expand and contract when subjected to varying pressures and temperatures and to compensate for design tolerances and yet which provides an effective and durable seal to prevent fluid from escaping from the joint. There is a self-evident need for the expansion joint to remain fully elastic and resist creep and relaxation at elevated temperatures; the stresses must also be low enough to avoid problems due to fatigue resulting from the cyclic deflections in the axial direction which the seal is intended to accommodate. This invention addresses these needs in the art, as well as other needs which will become apparent to those skilled in the art once given this disclosure.